Avian Influenza Disease

Worldwide, there are many strains of avian influenza (AI) virus that can cause varying degrees of clinical illness in poultry. AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be a natural reservoir for the less infectious strains of the disease.

AI viruses can be classified as highly pathogenic (HPAI) or low pathogenic (LPAI) strains based on the severity of the illness they cause. HPAI is an extremely infectious and fatal form of the disease that, once established, can spread rapidly from flock to flock and has also been known to affect humans. LPAI typically causes only minor illness, and sometimes manifests no clinical signs. However, some LPAI virus strains are capable of mutating under field conditions into HPAI viruses.

USDA’s Animal and Plant Health Inspection Service (APHIS) works to keep HPAI from becoming established in the U.S. poultry population.